TRUE RMS Digital Power Current Clamp Multimeter BENNING CM 12

Equipped with a data logger and Bluetooth® technology for app connectivity it is designed for sophisticated measuring tasks both in industry and trade.

For many years, current clamps have proved to be safe and reliable measuring devices for measuring current flows, without needing to disconnect the current-carrying conductors. Precise measurements that were initially only possible for sinusoidal alternating currents, but later also for direct current systems, are achievable today using modern measuring technology with the TRUE RMS measuring method or a switchable low-pass filter for high frequency suppression, even in industrial plants with non-linear loads.

POWER News (PN) spoke to Tobias Enck, a sales representative at BENNING's Testing and Measuring Equipment department, about the key features of today's current clamps, as well as their advantages and capabilities. The discussion focused on the BENNING CM 12 Digital Power Current Clamp Multimeter.

PN: A large number of current clamps are available on the market, each with several measuring functions and features. BENNING's MM 12 data logger and multimeter with connection to the app via Bluetooth has been available since 2017, and now the BENNING CM 12 Power Current Clamp has been added. What makes this so special?

Enck: Ultimately, it's the combination of numerous measuring capabilities, the wide measuring ranges and high basic accuracy, as well as the wide variety of switchable and selectable functions. The whole package of this data logging current clamp is totally rounded off, complete, and both functional and practical – designed to meet the highest demands.

PN: Let's go into detail and talk about the measuring functions. Which ones can the user particularly rely on?

Enck: The main functions are the current measurement of 10 mA to 600 A, the voltage measurement of 10 mV to 1,000 V and the combination of these measurements into the power measurement up to 600 kW. In addition, the power factor shows in the power measurement whether an inductive or capacitive load is present.

In electrical systems, e.g. where frequency transformers or pulsed motor drives are present, the switchable low-pass filter in the V AC and A AC function for high frequency (or RFI) suppression is a useful feature for filtering out high-frequency pulses.

A particularly useful form of current measurement with the BENNING CM 12 Power Current Clamp Multimeter is that of the inrush current that occurs immediately after switching on an electrical load and is measured over the first 0.1 seconds. It is often significantly higher than the rated current and puts a heavy load on the supply network and its components. Inrush currents mainly occur in transformers, motors, heating coils, light bulbs, DC/DC converters and in power supplies generally, where power-related voltage dips can occur. Cables, switches and relays must therefore be able to withstand these high currents without becoming damaged.

Probably the most important characteristic of high inrush currents is the accidental nuisance tripping of fuses and circuit breakers. If these inrush currents are known, due to being measured with the BENNING CM 12, the technician can immediately initiate appropriate countermeasures and install inrush current limits.

PN: A lot of people don't use, or know about, the ability to determine the network quality using the THD measurement function. Can you explain that in more detail to help our readers understand it better?

Enck: To assess the power quality, the BENNING CM 12 can be used to identify and display the total harmonic distortion (THD) and the distortion of individual harmonics up to the 25th harmonic wave. I would like to briefly explain the background to this. The constantly rising number of non-linear loads leads increasingly to 'network contamination'. More and more electrical consumers are taking a non-sinusoidal current from the grid. The Fast Fourier Transform (FFT) of the THD function disassembles the frequency components of the ‘contaminated’ current forms into a broad spectrum of harmonic frequencies. Harmonics are currents or voltages that have a frequency above the 50/60 Hz fundamental frequency and which are an integer multiple of this fundamental frequency. The current harmonics do not affect the active power – they only load the network thermally. As harmonic currents flow in addition to the active sine wave, this leads to an overload, a reduced lifespan and potentially even early failures of electrical consumers.

Harmonic loads are the cause of invisible voltage quality problems, which can lead to enormous costs for repairs and investments. The THD measurement determines the total harmonic distortion and shows the ratio of the actual effective value of all the harmonics to the actual effective value of the basic oscillation. This function is particularly useful in industrial environments.

The BENNING CM 12 is not a network analysis device but gives a first basic impression so that appropriate measures can be put in place. Passive components, but also modern 'active harmonic filters' help to eliminate harmonics.

The BENNING CM 12 is ideal for conducting series measurements, e.g. in battery rooms, due to its practical memory functions. The ability to quickly record and document measurement series is crucial.

PN: The term 'datalogger' forms part of the product name for a reason. What exactly are the memory function and data logger in this context and how do they work?

Enck: Multimeters and current clamps have some simple, but also transient memory functions such as the display of a minimum, maximum or average effective measured value. The HOLD function 'freezes' the latest measurement result so it can be read easily. The PEAK function shows the peak value of a measurement.

The measurement results that are recorded using the current clamp multimeter's MEM memory function are stored in an 'actual memory'. Here, measurement series of up to 1,000 measured values can be stored and read later via the display. These values can also be sent via Bluetooth to smart phones and tablets for further processing, using the free BENNING CM-MM Link app. The sub-function SAVE stores a measured value on key confirmation.

The A-SAVE variant can be used for voltage and resistance measurements. As soon as a stable measured value is detected by the measuring tips of the safety test leads, this emits a signal tone and the value is automatically transferred to the next free storage location. This enables successive series measurements to be made, e.g. in battery rooms. The significant advantages are immediate documentation and the speed at which measurement series can be recorded.

A data logger is a recording and storage method in which a sampling rate is set. In this way, up to 9,999 measured values can be written to the internal memory or transferred directly to the BENNING app via Bluetooth. The app display stores the measured values and presents them as a graph. Once a measurement series has been saved in the app, it can be forwarded to colleagues for joint evaluation.

PN: Aren't we now pretty far removed from the standard current clamp used by the electrical system installer?

Enck: Installation companies are becoming more specialised and increasingly support industrial electricians in the maintenance of industrial firms’ systems and equipment. In this case, the electrician is optimally equipped with a current clamp that has a measuring category of CAT IV 600 V suited to the industrial environment, with adequate measurement ranges, a generous clamp opening and the appropriate accessories.

PN: That all sounds very convincing. Is there anything else that has not been addressed that may be relevant to many of our readers?

Enck: This fully highlights the main advantages of the BENNING CM 12 Power Current Clamp Multimeter. In addition, there are the resistance and capacitance measurement functions, the continuity and diode tests, the bipolar phase sequence test, as well as the volt sensor located in the clamp head. The opening lever for opening and closing the current clamp also activates the measuring point and display illumination. The bar graph display is clearly visible in dark surroundings due to the backlight.

PN: The BENNING CM 12 Power Current Clamp Multimeter and BENNING MM 12 Multimeter are the highest quality measuring instruments in your range. What is your overall view of BENNING's position in the area of testing and measuring equipment?

Enck: Over the past ten years we have laid the groundwork very well and have continuously developed our products. We will, of course, continue to work on that. Today, we are represented on the market with a well-rounded and complete range, from the bipolar voltage tester to the installation and device tester.

We’re happy to answer any questions about testing and measuring technology, because as a matter of course, good customer-oriented and competent advice prior to purchase and comprehensive after-sales support are among our strengths.

PN: Mr Enck, thank you for the informative interview.

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